US2837655A

US2837655A - X-ray fluorescent analysis apparatus

Info

Publication number: US2837655A
Application number: US377098A
Authority: US
Inventors: Lang Andrew Richard
Original assignee: US Philips Corp
Current assignee: US Philips Corp; North American Philips Co Inc
Priority date: 1953-08-28
Filing date: 1953-08-28
Publication date: 1958-06-03
Anticipated expiration: 1975-06-03
Also published as: GB760448A; FR1106909A; DE1023246B

Description

June 3, 1958 A. R. LANG x-RAY FLUoREscENT ANALYSIS APPARATUS Filed Aug. 28. 1953 .5535,... m mmd mmHZDOO Jcoloml X-RAY FLURESCENT ANALYSIS APPARATUS Andrew Richard Lang, Tarrytown,`N. Y., assignor, by

mesne assignments, to North American Philips Company, Inc., New York, N., Y., a corporation of Dela- Ware Application August 28, 1953, Serial No. 377,698

11 Claims. (Cl. Z50-52) This invention relates to apparatus for analyzing X-ray fluorescent radiation.

A known method for conducting a quantitative or qualitative analysis of a material involves the excitation of the iluorescent or characteristic spectrum of the material by means of X-rays. This fluorescent radiation is then analyzed by a single crystal X-ray diffraction device in order to separate and measure the various component wavelengths of the fluorescent radiation. In such devices, a

Geiger-Mueller discharge tube, in conjunction with suitable counting circuits and a strip-chart recorder, is employed to record thev intensity and angular positions in degrees 20 of the reilections from the single crystal. Such a technique and apparatus is described, for example, yin U. S. Patent No. 2,449,066.

This known technique, however, suffers from certain limitations. vin particular", it has been found that the recorded results of this technique are often extremely complicated and difcult to analyze due to the fact that Several orders of reiiection from the same crystal. plane may be superimposed on one another. Moreover, the resultant pattern, if a strip-chart recorder is employed, will be replete with reflections which are not useful and therefore undesired, which further complicates the results and hinders a rapid and correct evaluation thereof.

Accordingly, the chief object of the invention is to provide an improved X-ray iluorescent analysis apparatus which enables rapid identification of the constituents, and their relative percentages, of the material under examination.

A further object of the invention is to render quan. titative analysis of a material by X-ray fluorescent analysis more accurate by eliminating, as much as possible, overlapping spectra.

A still further object of the invention is to provide an i improved X-ray iluorescent analysis apparatus in which the background is considerably reduced.

These and further objects of the invention will be best understood from the following description.

According to the invention, the X-ray fluorescent ana- I lysis apparatus comprises a source of X-radiation positioned to irradiate a specimen material with high-energy X-radiation to thereby evoke iluorescent radiation therefrom. A single-crystal goniometer is provided `to sep- Varate and analyze the iluorescent radiation emanating States Patent corded in a conventional manner by a counting rate meter or strip-chart recorder.

In accordance with a further aspect of the invention, the entire apparatus is made completely automatic by providing means for synchronizing the goniometer scanning motion and the mean channel height of the pulse analyzer in a predetermined manner whereby a complete scan of the specimen-matenal-iluorescent radiation can be obtained in which only rst order reilections are present. The synchronizing means are preferably constituted by anpotentiometer in the pulse analyzer circuit mechanically linked to the goniometer scanning motor so as to be uniformly rotated thereby, but having a coil winding thereon adapted to produce a sliding mean channel height corresponding. to a cosecant function. Alternatively, however, the synchronizing means may be constituted by a linear potentiometer in the pulse analyzer circuit which is driven by a mechanical device adapted to exhibit a cosecant function motion.

This construction has the advantage that the recorded `results of the examination of the specimen material are materially simplifiedv thereby facilitating rapid identification of its constituents. That is to say, the only pulses or peaks recorded by they strip-chart recorder will be those performing a useful function in enabling the operator to identify the constituents of the material. Most other extraneous peaks, which normally serve to cornplicate the final analysis by the operator, will have been eliminated. Moreover, a considerable reduction in background on the chart will be effected. Finally, since this construction enables the study of only one order of rellections at a time, the number of peaks due to the exciting radiation appearing on the record is advantageously diminished. n

. The invention will now be described in connection with the accompanying drawing in which:

Fig. l shows a schematic View of one form of X-ray fluorescent analysis apparatus in accordance with the invention;

Fig. 2 is a graph of the energy content of the fluorescent radiation of first order reilections with rotation of the detector arm of the goniometer in terms of 20 angles. l

Referring now to Fig. 1 of thedrawing, a specimen material it), which is to undergo a qualitative or quantitative examination, is positioned in the path of X-radiation 11 from an X-ray tube l2 or other source of X-radiation. By a suitable choice of the quality of the X-radiation il, the specimen itl can be caused to lluoresce or emit its characteristic spectrum. A portion of this characteristic spectrum is collected by a collimator 16, which may consist of a plurality of fine parallel coaxial tubes to limit divergence of the iluorescent radiation l5 in all planes, and transmitted to a goniometer device 2t).

The goniometer 20 comprises a rotatable single crystal 21, e. g. of rock salt or quartz, an auxiliary collimator 22, and a rotatable detector 23. The auxiliary collimator 22, which may also compriseia plurality of coaxial fine parallel tubes, is linked to the detector 23 Such that rotation of the detector 23 carries along the collimator 22. The single crystal 2l is also adapted to rotate about an axis 2a, and its rotation speed is chosen, in the conventional manner, to be one-half the speed of the detector 23.,

The detector 23,V in accordance with the invention, is

constituted by a proportional counter, i. e., an X-ray responsive device capable of producing an electrical signal having an intensity. or amplitude corresponding to the energy content` of the iluorescent radiation reflected otr the signal crystal face 2l. This proportional counter 23 may take many different forms. For example, it Ymay be a Geiger-Mueller tube operated in the portional region of its discharge characteristic, below the threshold potential. Alternatively, it may be a crystal detector, the socalled scintillation counter, which is responsive to X- radiation and produces an electric signal of varying am plitude corresponding to the energy content of the fluorescent radiation.

The electrical signals produced by the proportional counter 23 are then passed through a discriminator or pulse height analyzer 26 adapted to transmit all electrical signals having amplitudes falling within a channel of amplitudes fixed by the analyzer, and to intercept or block all othersignals. For this purpose, the analyzer 26 would have provision, usually in the form of

adjustable potentiometers

27, 28, for determining the width and mean height, respectively, of the channel of signal amplitudes which will be permitted to pass through. These selected signals are then counted and recorded in the conventional manner by, for example, a stripchart recorder 29 or a counting rate meter. Where a strip-chart recorder is employed, the results will appear as a plot of peak signalintensity with scanning angle The apparatus shown in Fig. l operates in the following rnanner: The specimen l@ is placed in position and subjected to intense irradiation from the X-ray tube l2, thus exciting the constituents of the specimen into fluorescence. A portion l5 of that fluorescent radiation is collected by the collimator 16 and transmitted to the analyzing crystal 2l of the goniometer. At each angular position in degrees 26 of the crystal 2l, those wavelengths of the impinging fluorescent radiation which fulfill the Bragg equation nk:2d sin 0 will be diifracted or reflected onward in the direction of the proportional counter 23. The reflected beam is collimated by the auxiliary collimator 22 and collected by the counter 23, which thereupon produces electrical signals of an intensity proportional to the energy content of the reflected fluorescent radiation. The goniometer is usually arranged to scan the fluorescent radiation from the specimen over a wide angular range of angles, thereby producing, on the recorder 29, a chart containing a plurality of peaks of differing intensity located at particular angles in degrees 26, each specific peak or group of peaks characterizing a given element of the periodic table, and the intensity or amplitude of the peak determining the quantity of that element in the specimen.

The recorded peaks, however, in the absence of the pulse analyzer, represent, usually, first order reflections (11:1 in the Bragg equation) including the Ka, K, Lot and L lines; second order reflections (11:2) including K and L lines; and some third order reflections (11:3) of the K lines. In most cases, only the first order reflections are necessary in order to effect complete identification of the specimen constituents, reflections from higher orders serving merely to confuse and complicate the pattern, and, in some instances, serving to obliterate a useful first order reflection.

Accordingly, by passing the electrical signals from the proportional counter 23 through the pulse height analyzer 26, those undesirable higher order reflections may be eliminated, due to the fact that their energy contents are usually much larger than the energy content of the first order reflections which have associated with them longer wave lengths. Consequently, the proportional counter 23 in conjunction with the pulse height analyzer 26 affords a mechanism for discriminating between reflections of different orders. The floor of the channel erected by the pulse analyzer may be set by adjustment of the

potentiometers

27, 28 to a value slightly belowk the energy content of the first order reflections, and the y in 20.

ceiling of that channel adjusted to a value below the energy content of the 2nd order reflections. Alternatively, the mean channel height 28 could be adjusted to the average value of the energy content of the 1st order reflections, and the channel width 27 adjusted to include a small area on either side of the average energy content.

It has been found, however, that with increasing values of the scanning angle of the goniometer in degrees 20, the first order reflections decrease in energy content in accordance with a cosecant function. That is to say, the Bragg equation n)\:2d sin 6 can be reduced for a particular analyzing crystal and a given reflection order to the proportionality ?\:sin 0. However, the energy content of E of X-radiation is inversely proportional to its wave-length, i. e.,

E -.L @cosecant 6 sin 9 Stated otherwise, for a given reflection order, the energy content of the reflected fluorescent radiation decreases as a cosecant function of the scanning angle 0.

Accordingly, in order to insure the transmission of all first order reflections through the pulse analyzer 26, the mean channel height will have to be adjusted for each angle of the goniometer in degrees 29. This is graphically illustrated in Fig. 2 of the drawing, which depicts a graph of energy content E along the ordinate and angular positions in degrees 20 along the abscissa. The solid line curve 40 represents the cosecant function decrease in energy content of first order reflections with an increase The dotted lines 41, 42, on either side of the solid line curve, depict the sliding channel which must be produced by the pulse analyzer 26 in order to transmit all the first order reflections. As will be noted, the lchannel width of the analyzer 26 may be maintained constant, but the mean channel height should slowly decrease as the goniometer scanning motion traverses its path over the required angular range.

This synchronized motion between the goniometer scanning motion and the mean channel height of the pulse analyzer may be effected in a number of different ways. A preferred arrangement involves the replacement of the ordinary linear potentiometer of the pulsek analyzer, which serves as a channel height adjuster, by a potentiometer 28 having a special winding adapted, upon uniform rotation of the potentiometer, to produce the desired ychange of mean channel height with degrees 29 of the goniometer as shown in the curve 40 of Fig. 2. ln this case, the potentiometer 28 may be directly linked by means of a suitable gear box 45 to the same motor 30 that drives the goniometer. The winding of the potentiometer need not produce a channel height adjustment which exactly corresponds to the curve 4l) of Fig. 2. In most cases, the approximation obtained from two linear motions, as shown in the dash-dot curves 44 of Fig. 2, will be adequate. Therefore, two uniformly wound sections on the potentiometer 28 will suffice.

Alternatively, a linear potentiometer 28 may be employed, and be driven by any one of many well-known mechanisms capable of providing a substantially cosecant function motion suitable to obtain the sliding channel height variation desired. This mechanism can, of course, also be linked to the goniometer scanning motion.

While we have described our invention in connection with specic embodiments and applications, other modifications thereof will be readily apparent to those skilled in this art without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

l. An X-ray fluorescent analysis apparatus comprising an X-ray source for producing X-radiation, means for supporting a specimen material in a position to receive said X-radiation to excite uorescent radiation therein, and means for separating and analyzing the fluorescent radiation produced by said specimen; said analyzing means comprising a goniometer including a single crystal and a radiation detector for scanning the uorescent radiation emanating from said specimen, said radiation detector being a proportional counter adapted to translate X-radiation into electrical signals, pulse analyzing means coupled to said proportional counter and responysive to electrical signals having an amplitude Within a given range and of a given mean amplitude, means for varying the mean amplitude response of said analyzer, and means coupling said amplitude adjusting means to said goniometer for synchronizing the scanning motion of the goniorneter and the mean amplitude response of said analyzer to eliminate substantially al1 but rst v pled to said proportional counter and responsive to electrical signals having an amplitude Within a given range and of a given mean amplitude including means for varying the mean amplitude response of said analyzer, means for decreasing the mean amplitude response of said analyzer in accordance With a cosecant function as the goniometer scans the fluorescent radiation in the direction of increasing angles, and means coupled to the output of said pulse analyzer to indicate the quantity of electrical signals produced therefrom.

3. An X-ray uorescent analysis apparatus comprising an X-ray source for producing X-radiation, means for supporting a specimen material in a position to receive said X-radiation to excite fluorescent radiation therein, and means for separating and analyzing the iluorescent radiation produced by said specimen; said analyzing means comprising a goniometer including a single crystal and a radiation detector for uniformly scanning the fluorescent radiation emanating from said specimen over a given angular range in degrees 20, said radiation detector being a proportional counter adapted to translate X-radiation into electrical signals, pulse analyzing means coupled to said proportional counter and responsive to electrical signals having an amplitude Within a given range and of a given mean amplitude including means for varying the mean amplitude response of said analyzer, and means for synchronizing the scanning motion of the goniometer and the mean amplitude response of said analyzer to eliminate substantially all but rst order reflections from the single crystal, said synchronizing means imparting to said analyzer a cosecant function variation with scanning angle of the mean amplitude response thereof.

Il. An X-ray fluorescent analysisapparatus comprising an X-ray source for` producing X-radiation, meansfor supporting a specimen material in a position to receive said X-radiation to excite lluorescent radiation therein, and means for separating and analyzing the uorescent radiation produced by said specimen; said analyzing means comprising a goniometer including a single crystal and a radiation detector, means for uniformly rotating said single crystal and said radiation detector to scan the fluorescent radiation emanating from said specimen over a given angular range in degrees 20, said radiation detector being a proportional counter adapted to translate X-radiation into electrical signals, pulse analyzing means coupled to said proportional counter and responsive to electrical signals having an amplitude Within a given range and of a given mean amplitude, means for varying the mean amplitude response of said analyzer relative to the position of the goniometer, means coupling said amplitude adjusting means to said goniometer for synchronizing the scanning motion of the goniometer and the mean amplitude response of said analyzer to eliminate substantially all but iirst order reflections from the single crystal, and indicating means coupled to said pulse analyzer to indicate the quantity of electrical signals produced therefrom.

5. An X-ray fluorescent analysis apparatus as claimed in claim 4 in Which the proportional counter is constituted by a Geiger-Mueller tube adapted to be operated in the proportional region of its discharge characteristic.

6. An X-ray fluorescent analysis apparatus as claimed in claim 4 in which the proportional counter is constituted by a scintillation counter.

7. An X-ray fluorescent analysis apparatus comprising an X-ray source for producing X-radiation, means for supporting a specimen material in a position to receive said X-radiation to excite fluorescent radiation therein, and means for separating and analyzing the iluorescent radiation produced by said specimen; said analyzing means comprising a goniometer including a single crystal and a radiation detector, means for uniformly rotating said single crystal and said radiation detector to scan the uorescent radiation emanating from said specimen over a given angular range in degrees 26, said radiation detector being a proportional counter adapted to translate X-radiation into electrical signals, pulse analyzing means coupled to said proportional counter and responsive to electrical signals having an amplitude Within a given range and of a given mean amplitude including a potentiometer for varying the mean amplitude response of said analyzer, saidpotentiometer having a Winding arranged to impart a decreasing cosecant function variation of the mean amplitude response of said analyzer upon rotation, means for uniformly rotating said potentiometer to synchronize the scanning motion of the goniometer and the mean amplitude response of said analyzer to eliminate substantially all but first order reflections from the single crystal, and counting and recording means coupled to the output of said pulse analyzer to record the quantity of electrical signals produced therefrom.

8. An X-ray fluorescent analysis apparatus as claimed in claim 7 in which the means for rotating the single crystal and detector and the means for rotating the potentiometer are linked together.

9. An X-ray fluorescent analysis apparatus as claimed in claim 7 in which the proportional counter is constituted by a Geiger-Mueller tube adapted to be operated along the proportional region of its discharge characteristic.

10, An X-ray iiuorescent analysis apparatus comprising an X-ray source for producing X-radiation, means for supporting a specimen material in a position to receive said X-radiation to excite fluorescent radiation therein, and means for separating and analyzing the uorescent radiation produced by said specimen; said analyzing means comprising a goniometer including a single crystal and a radiation detector, means for uniformly rotating said single crystal and said radiation detector to scan the lluorescent radiation emanating from said specimen over a given angular range in degrees 20, said radiation detector being a proportional counter adapted to translate Xradiation into electrical signals, pulse analyzing means coupled to said proportional counter and responsive to electrical signals having an amplitude within a given range and of a given mean amplitude including a linear potentiometer for varying the mean amplitude response of said analyzer, means for imparting a cosecant function rotation to said potentiometer for synchronizing the scanning motion of the goniometer and the mean amplitude response of said analyzer to eliminate substantially all Q but first order reflections from the single crystal, and counting and recording means coupled to the output of said pulse analyzer to record the quantity of electrical signals produced therefrom.

11. An X-ray fluorescent analysis apparatus as claimed in claim 10 in whichthe proportional counter is constituted by a Geiger-Mueller tube adapted to be operated in the proportional region of its discharge characteristic.

ReferencesvCited in the le of this patent UNITED STATES PATENTS Harker Feb. 6, 1951 Hamacher Nov. 25, 1952 Youmans et al Nov. 10, 1953 Gossick Iuly 6, 1954 Herzog June 21, 1955